1. Field of the Invention
The present invention relates to a method of producing a laminated metal belt from a laminated metal sheet material which is installed on a drive pulley and a driven pulley for transmitting power.
2. Description of Related Art
FIG. 1 is a schematic view of the state wherein a ring laminated metal belt 1 is used. The ring laminated metal belt 1 is used not only for transmitting power but also be used in a nonstep variable speed gear which is able to adjust the running speed freely while maintaining constant revolutions of the pulley 2, by making radii r, R of pulleys 2, 3 adjustable to which the ring laminated metal belt 1 is installed.
The ring laminated metal belt 1 installed on the pulleys 2, 3 has a portion bent at a predetermined radius r or R and a portion stretched straightly between the pulleys 2, 3, so that repetitive bending and restoring deformation is applied on the belt by the rotation of the pulleys. Thus, the belt must be sufficiently flexible against bending and having a necessarily sufficient strength against the tension for transmitting power. As a material of such a belt, various kinds have been proposed hitherto, and for example, fiber reinforced rubber, a firmly woven fiber, leather etc. have been widely used.
However, though these belts of nonmetal material are flexible and sufficiently endurable to the repetitive bending and restoring deformation, tensile strength per unit sectional area is limited. Thus, when the large power is to be transmitted, it is forced to apply a wider belt, install plural belts in multiple or the like, which results in a large space occupied by the pulleys and the traveling belt therebetween, and further the weight of the pulley itself becomes heavier. Accordingly, for such use as a nonstep various speed gear of an automobile where the installing space is limited, the light weight and high reliability on the break proof are required, a nonmetal belt can not be used and the strong metal belt must be employed.
Also in this case, the structure and material which do not create the fatigue fracture by the repetitive bending and restoring are naturally required.
The metal belt is used generally in the laminated state wherein a plurality of ring belts, each peripheral length being slightly different, are fitted inwardly or outwardly. The fitted condition between the adjoining ring belts is adjusted to develop a relative slide circumferentially with a moderate frictional resistance, so as to create a slide between the ring belts during the repetitive bending and restoring deformation, and not to produce excessive tensile and compressive stresses on the individual ring belt. The reason why the plurality of ring belts are laminated is to secure enough entire sectional area of the belt to prevent the tensile fracture of the belt used by applying the tension.
The thinner the ring belt, the smaller the tensile stress and compressive stress due to bending and restoring, thus the bending and restoring fatigue fracture hardly occurs. Accordingly, it is not necessary to use such a strong material. However, since a production cost is increased by making the ring belt thinner, the thickness of the ring metal belt is set around 0.2 mm currently. In this thickness, maraging steel is required from the viewpoint of the strength against fatigue, besides generally the hardening heat treatment by aging and so forth or further the surface hardening heat treatment by nitriding and so forth are performed.
A conventional method of producing a ring laminated metal belt is divided roughly into a method of using a sheet material and a method of using a seamless steel pipe material.
In the former method disclosed, for example, in Japanese Patent Application Laid-Open No. 57-161335 (1982) and Japanese Patent Application Laid-Open No. 58-159937 (1983), end portions of a band sheet material having the same thickness, width and length of one ring belt constituting a laminated belt are butted and welded together into a ring. After the heat treatment for unifying the strength of the welded portion and the other portion, it is finished into a predetermined thickness and peripheral length by ring rolling, then hardened by the heat treatment and formed into a ring, a plurality of which are fitted in multiple into a laminated belt.
In the latter method, a seamless steel pipe having a predetermined thickness and outside diameter is cut into section to the width corresponding to one ring belt, and after annealed, if necessary, finished into a predetermined thickness and peripheral length by ring rolling, then hardened by the heat treatment and fitted in multiple into a laminated belt.
The plural ring belts constituting one unit of laminated belt are so produced that every ring belt has a different peripheral length to be fitted in multiple. However, as previously stated, a delicate fitted condition must be maintained all around the peripheral to create the relative slide with a moderate frictional resistance between the adjoining rings. Obtaining such fitted condition by only adjusting the thickness and peripheral length in ring rolling, a great deal of labor is required and productivity is considerably spoiled.
Also, the thinner the ring belt the more delicate the thickness reduction adjustment for adjusting the peripheral length, thus not only an enormous amount of work is necessitated but also yield of non-effective unit extremely lowers.
As a countermeasure, a circumferential expanding method has been proposed to stick the adjoining ring belts together moderately, after plural ring belts are combined to form one unit of laminated belt. For example, such a method by split tools disclosed in Japanese Patent Application Laid-Open No. 56-30041 (1981) and Japanese Patent Application Laid-Open No. 56-84139 (1981), or a method by heat expansion of a core metal disclosed in Japanese Patent Application Laid-Open No. 57-163750 (1982).
Even by these methods, however, it is difficult to accomplished a delicate size adjustment at 1/100 mm level perfectly. Therefore, as stated in Japanese Patent Application Laid-Open No. 58-118351 (1983), a method has been devised to prepare a belt once in which the ring belts are joined together, then decompose them to polish chemically, and after reduction in thickness to obtain the moderate fitted condition combine them again. However, there is such a problem in any of the methods aforementioned that a great deal of labor is necessitated in adjusting the fitted condition between the adjoining ring belts.